Suppressor electrode for depressed electron beam collector

ABSTRACT

A rugged unitary electron beam collector structure for a velocity modulation or other high power electron beam vacuum tube is characterized by the use of a ruggedly mounted suppressor electrode at the entry of the collector permitting reliable, high efficiency operation. The improved structure is constructed of stacked ceramic and metallic elements bonded together in a configuration also providing improved tolerance to thermal and mechanical shock.

m1 3,824,425 [451 July 16, 1974 United States Patent [191 Rawls, Jr.

SUPPRESSOR ELECTRODE FOR DEPRE-SSED ELECTRON BEAM COLLECTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to means for improving the efficiency and life-time of operation of a beam power electron tube and more particularly concerns a rugged electron suppressor electrode for operation with a depressed potential electron beam collector in a velocity modulation high frequency power vacuum tube.

2. Description of the Prior Art Several types of high frequency power vacuum tubes exist that employ an electron beam having high density electron currents driven at high velocities, such as velocity modulation tubes of the traveling wave or klystron type. ln such devices, production and acceleration of the electron beam occurs in a cathode-anode region and then the beam passes into a separate region in which its kinetic energy is used in part to amplify high frequency electromagnetic fields. ln many early designs of such tubes, the electron beam, still having quite high kinetic energy, passes on out of the high frequency interaction structure and is dissipated in a third region as heat in a collector electrode held at about the same potential with respect to ground as the interaction structure.

It has been shown that the over-all efficiency of such beam tubes may be considerably increased by the use of specially designed electron beam collectors operated at potentials considerably below the potential of the high frequency interaction structure. Such collectors are known as depressed collectors and have permitted improved use of the total kinetic energy of the electron beam. Also, with greatly reduced heating of the collector, considerably less power is lost for cooling the collector and simple air cooling systems are often sufficient replacements for the previously needed complex liquid cooling systems. X-radiation is also reduced, permitting reduction in shielding against its destructive properties and therefore decreased weight.

Ideally, such a collector, to be fully efficient, must capture electrons over a broad range of velocities and so would be made up of a plurality of collector electrodes, each operating at its particular depressed po- SUMMARY OF THE INVENTION The present inventionis a rugged electron beam collector of unitary character having a suppressor electrode at its entry permitting reliable and long life operation of a velocity modulation tube at high power and high efficiency. The invention is characterized by the presence of a ruggedly mounted suppressor electrode system operated at a potential below the potential of the electron tube high frequency interaction structure in a unitary beam collector so that a significant portion of the kinetic energy remaining in the electron beam as it exits from the high frequency interaction region may be recovered rather than lost as heat. The simple ruggedly supported suppressor electrode, operated at a potential slightly negative with respect to that of the collector electrode, permits use of the unitary collector in a tube having substantially the efficiency of a tube with the much more complex multi-electrode collector. The novel depressed electron collector and suppressor electrode system is constructed of an array of similar ceramic and metal elements bonded together in a manner providing reduced shear forces on ceramic-to-metal bonds and accordingly affording ease of manufacture and long life operation of` the vacuum tube assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory schematic representation of a velocity modulation tube employing the novel suppressor and depressed collector electrode system.

FIG. 2 is a cross section view of a preferred embodiment .of the invention.

DESCRIPTION OF THE PREFERRED VEMBODIMENT FIG. 1 represents schematically an electron beam type of velocity modulation tube embodying the electron beam collector improvement of the present invention and showing operating circuit connections. While FIG. 1 schematically illustrates a helix travelingvwave velocity modulation tube, it will be recognized by those skilled in the art that other known high frequency slow wave propagation elements may be substituted for the helix high frequency interaction circuit. Further, it will be recognized that other high frequency interaction circuits may substituted for the helix, including the cavity resonator systems characteristic of the klystron, such alternative arrangements being illustrated, for example, in U.S. Pat. No. 3,172,004, entitled Depressed Collector Operation of Electron Beam Device, issued Mar. 2, 1965 to Messrs. R. J. Von Gutfeld and C. C. Wang and assigned to the Sperry Rand Corp.

In FIG. l, heater filament l is caused to heat the surface of the emitter cathode or electron beam forming means 2 by electrical current flowing from electrical source or battery 3. The cathode system is held at a negative potential with respect to ground by the cathode supply source 4. Consequently, a lineal electron beam 5, usually of circularly symmetric character, is projected through van aperture in the grounded anode 6. Beam 5 flows in conventional enery-exchanging relation through a grounded high frequency energy exchanging device or helix 7 having respective input and output transmission line terminals 8 and 9 for example. Electrons passing out of helix 7 and through grounded apertured diaphragm 20 after exchanging energy with the traveling high frequency fields within helix 7, are collected by electron beam-collector electrode l0. Such is accomplished with collector l0 at a potential considerably depressed with respect to the ground potential of helix 7 by virtue of collector electrical potential source or battery ll, one side of which is connected via terminal 14 to collector l0 and the other via lead 12 to junction 13 between cathode supply source 4 and cathode 2.

As previously noted, velocity modulation tubes with a single-element collectorsuch as the unitary collector l0 of FIG. l operate with the collector l0 placed at a compromise voltage; i.e., at a voltage level with respect to ground such that a majority of the electrons remaining in beam 5 are slowed down and are collected, their kinetic energy being returned to the power supply system. Evidently, electrons of certain speeds may not be collected and can, in fact, be disadvantageously returned to the interaction region within helix 7. For example, low velocity primary electrons attempting to enter collector for the first time and secondary electrons generatedA in collector l0 and migrating therefrom may, for certain collector voltages, be moved back into the interaction region to strike the helix 7 adjacent output 9,vcausing the helix to overheat and even to melt under particularly adverse conditions. Multiple element collectors, where several electrodes are operated at progressively different depressed voltages, have demonstrated relatively efficient collection of electrons over the large spectrum of velocities normally present, but such devices make the vacuum tube more expensive and heavier and also require more complex power supply equipment.

According to the present invention, there is used between the output end 9 of helix 7 and collector 10 a ruggedly supported apertured suppressor electrode 16 For example, a velocity modulation tube employing the novel rugged suppressor electrode 16 may operate with an electron beam acceleration voltagev between cathode 2 and ground or anode 6 of substantially 12,000 volts. Such an electron beam may be collected in a collector 10 operating at 7,000 volts with respect to ground. The suppressor electrode 16 may be made to operate efficiently with a battery 17 supplying 1,000 volts, for example. Since the stray electrons are mainly returned by suppressor electrode 16 to collector 10, rather than being collected by electrode 16, only small currents flow through battery or supply 17, and a relatively low level power supply is required. The operation permits the collector voltage to be relatively more depressed,v thus improving the efficiency of the power supply system without subjecting the tube to overheating and without the need for a multi-element collector. It is to be understood that the cited electrical potential values are to be taken merely as representative examples and are not necessarily intended as limiting or optimum values for operation of a traveling wave, klystron, or other beam power tube according-to the invention.

FIG. 2 represents a preferred embodiment of the invention in which apertured diaphragm 20 may be spoken of as lying in a plane between old and new parts of a representative traveling wave amplifier tube embodying the invention. As is generally illustrated in the above mentioned Von Gutfeld et al. U.S. Pat. No. 3,172,004, diaphragm 20 and parts to the left of diaphragm 20 such as vacuumenvelope 19'are conventional parts to be recognized as being assembled in the manner they are used in prior art traveling wave amplifier devices. Parts to the right of diaphragm 20 make up the novel depressed collector and suppressor electrode structure of the present invention. lt is to be observed that aperture 2l is aligned with the axis of the electron beam 5 of FIG. 1 and that beam S, after having inter acted with high frequency fields, such as those within helix 7 of FIG. l, passes through aperture 2l of FIG. 2 into the novel collector system.

Electron beam 5 is actually stopped or collected by the generally symmetric interior walls of hollow electron beam-collector-core 22, these inner walls being provided by cooperatingv axially aligned and axially extending interior sections forming wall portions 22a to 22d. The core 22 may be made of a material such as oxygen-free copper. AWall portion 22a is in the form of a frustrum of a cone. It is joined at its small diameter end to a circularly cylindric wall portion 22b. Wall portion 22b is ultimately joined to a second and smaller diameter circularly cylindric wall portion` 22d. The remote end of wall portion 22 is closed.

The collected electron beam current may be drawn from-hollow core 22 via lead wire 14 which may also be comprised of copper and may be fastened by any of several known suitable means at 14a to the outer end of core 22. The collected current, as suggested in FIG. 1, may be drawn off at a voltage which is negative with respect to the voltage on helix 7 and which is typically 40 to 60 per cent of the voltage supplied to cathode 2.

The progressively decreasing diameters of axially extending interior walls 22a to 22d permit each such wall section to collect substantially the same fraction of the total electron beam current. Thus, the portions of the total remaining kinetic energy of the electron beam S converted to heat at the several wall sections 22a to 22d are substantially equal. As a consequence, such heat is relatively evenly distributed along the length of co're 22.

Core 22 is supported within an outer jacket or generally cylindric vacuum envelope wall or casing means 24, also constructed of a metal such as oxygen-free copper. One end of wall 24 is closed by diaphragm 20 sealed at its periphery to casing means 24, for example, by a circular brazed junction 26.

A drawn cup-shaped metal end cap 25 is fastened at the opposite or outer end of wall or casing means 24 by a circular brazed vacuum tight junction 27. End cap 25 is of sufficient volume to accommodate collector lead 14, which is .formed with a right angle bend and projects out of the interior of cap 25 through insulator 29. Insulator 29 may be formed of any of several available ceramic materials having good high-voltage insulation properties and adapted to form a vacuum tight seal with the metal at cap 25 at circular junction 30. Lead wire 14 is similarly sealed within a hole in insulator 29 at surface 28. Although other materials may be used, certain nickel-iron-dhromium alloys have been found to be useful for cap 25, since they are capable of being generated by drawing and since they readily form vacuum tight seals with ceramic materials.

From the foregoing, it is apparent that diaphragm 20, outer wall orcasing 24, cap 25, and insulator 29 complete the vacuum envelope means of the high frequency tube structure embodying the invention. Wall 24 has additional significant functions, in that it cooperates in the support of core 22 by means providing high electrical voltage insulation along radial, low thermal impedance, heat flow paths from core 22 to wall 24, as is particularly described and claimed in the J. L. Rawls U.S. Pat. application Ser. No. 54,943 for "Depressed Electron Beam Collector, filed `luly 15, 1970, now U.S. Pat. No. 3,662,212 assigned to Sperry Rand Corp. Al suitable alternative collector and collector support system is found in the T. R. Doyle U.S. Pat. application Ser. No. 173,053 for Compact Depressed Electron Beam Collector, filed Aug. 19, 1971, now U.S. Pat. No. 3,717,787 and also assigned to the Sperry Rand Corp. In devices of this character, heat may be conducted directly inv radial paths from the outer cylindric surface 34 of core 22 by a series of generally circular outwardly extending apertured flexible fins 32 and 33 to 33d, the latter of which are fastened at substantially equal intervals to wall surface 34, as brazing. Fin 32 is of a distinctive type, being formed integrally of oxygen-free copper with a discrete input section 35 of core 22, the apertured electron beam input section 35 as bengfastened by brazing to core 22 at junction 26. As the electron beam 5 flows through aperture 21 in a diaphragm 20, it may tend to spread due to space charge effects while passing through the somewhat larger aperture 37 of input section `35'and into the interior of core 22.

Fins 32 and 33 to 33d act as flexible support means and are spaced at substantially equal intervals, fins 33 to 33d being of generally similar structure. Typical of the latter group of fins is fin 33 which is seen to include an inner dished section 38 in the general form of a frustrum of a conical shell, the base of the conical shell being affixed to surface 34. The apex of the conical shell isdirected toward the high frequency interaction circuit 7. As noted previously, the apertured wall 39 of dished section 38 may be brazed to the surface 34 of core 22. Fins 33a to 33d are similarly shaped and fastened and may include drilled-out holes, such as hole 40 in fin 32, for permitting the exhaust of gas from the interior of collector when the vacuum tube is going through its final processing during manufacture. A longitudinal slot 4l may also be milled in the surface 34 of core 22 for the purpose, slot 4l extending from the vicinity of the end of core 22 supporting lead 14 to an interior portion of the tube served by hole 40 during exhaust.

A second array of seven generally similar apertured flexible fins', made also of oxygen free copper, extends cooperating support inward from the inner cylindric surface 24a of jacket wall 24, but does not directly contact wall 34 of core 22. The inner diameter of aperture 43 in the typical fin 42, for example, is considerably greater than the outer diameter of core 22, thus providing a substantial electrical clearance between core 22 and fin 42. Typical also of the array of flexible support fins 42 and 42a to 42f is the dished portion 44 of fin 42 in the general shape of a frustrum of a conical shell, the outer circular edge of portion 44 being brazed to the inner wall surface 24a or otherwise fastened thereto. The dished fin portions 44 may be equipped with drilled-out holes such as typically represented by hole 45 in-fin 42 for the purpose of aiding evacuation of the vacuum envelope of the tube, including the interior of cap 25, during manufacture. Fins 42 to 42f are spaced substantially equally along wall surface 24a and are alternately interwoven with the Aarray comprising fins 32 and 33 to 33d. The separations between the successive inward and outward extending fins are substantially equal.

Such equal spacings are designed to accommodate substantially equal width, spaced, flat-sided, insulator rings 46 to-46k between the flat sided parallel wall porf tions of the inward and outward extending arrays of fins. Rings 46 to 46k may be formed of any of several available ceramic materials having good electrical insulation properties, suitable mechanical and thermal properties, and adapted to form a permanent shock resistantbond with the sheet copper of which the vfins of the two fin arrays are constructed.

For ex'ample,flat sided annular ring 46 is a representative element of the fin-insulatorfin structure. Ring 46 may be made of an aluminum oxide ceramic or of certain. other well known refractory oxide materials, such as beryllium oxide. The annular flat sides 50a, 50b, of ring 46 are coated with nickel using a standard metal coating method. Surface 50a is placed on the flat annular face of inward extending fin 42. In turn, the outwardly extending fin 32 is placed on surface 50b. Additional con'ventional heating and other steps are taken to form permanent,mechanically sound bonds at surfaces 50a and 50b between vceramic ring 46 and the respective fins 42 and 32. A similar pair Vof bondsl is formed between ceramic ring 46a and fins .32 and 42a, between ceramic ring 46h and-fins 42a and 33, between ring 46c and fins 42a and 33a, and so forth on along the assembly to ceramic ring 46k whose'flat sides are similarly bonded to fins 33d and 42f.

For permitting the unitary collector core 22 and its support system to operate with maximum collector voltage depression and for permitting the velocity modulation tube employing it to operate with maximum acceleration voltage and reliability with freedom from internal damage due to overheating, the novel ruggedly mounted suppressor electrode 16 is used. Electrode 16 may be made of molybdenum or of a nickel-iron alloy,

is supported in electrically insulated relation from diaphragm 20, and has an aperture 50 aligned along with the axis of symmetry of the tube'with the aperture 21 in diaphragm 20 and also with entrance aperture piece 35 of collector core 22, so that the electron beam v5 passes in succession through apertures 21 and 50into core 22. Electrode 16 includes a flatouter section and an inner dished section 5l defining the aperture 50, section 5l being in thev general form of afrustrum of a conical shell, electrode 16 being generally similar in shape to fin 42.

For supporting suppressor electrode 16 in a rugged manner with respect to the interior collector l0, a support ring 52 is employed having respective offset inner and outer annular flat portions 53 and 54, annular portion 54 defining a large aperture 50 that is concentric with the axis of the tube. Support ring 52 may be made of a nickel-iron alloy and a free surface of the ring is symmetrically welded by a helium arc or is spot welded to the interior surface of diaphragm 20.

Suppressor electrode 16 is fixed in position concentrically about the tube axis by an annular, flat-sided, insulator ring 55. Ring 55 may be lformed of any of several available ceramic materials such as beryllium or aluminum oxide, having good electrical insulating properties and adapted to form permanent, shock resistant bonds with the materials of ring 52 and electrode 16. Such bondsmay readily be formed by affixing a metal layer to each of the flat sides of ceramic ring 55, then by completing the seals in the conventional manner by brazing.

Battery 17 may be coupled to suppressor electrode 16 by lead wire 19 which passes in brazed or otherwise ramic material and is spot welded at 56 at the periphery of electrode 16'. The outer cylindrical surface Aof ceramic cylinder 57 is sealed in vacuum tight vrelation to the inner surface of av conventional flanged `tube 59. Tube 59 is soldered at flange 60 tothe envelope 24 of collectoral. Other conventional arrangements maybe used for supplying the required operating potential to suppressor electrode 16.

ln the operation ofa traveling wave tube employing a unitary electron beam collector 22 without provision of the novel suppressor'electrode 16, the electron beam 5, after having supplied energy to the high frequency fields propagating on 'helix 7, leaves the interaction region through aperture 21. Many of the individual electrons in beam have been substantially. reduced in velocity by the' forcesofinteraction. Particularly', the

slower electrons begin to migrate radially out of the bonds of the suppressor and collector are significantly reduced, permitting long life of the vacuum tube strucis wasted inthe form of heat. Also, any reflected'primary or secondary electrons exiting from collec-tor 22 are similarly collected at ground potential.

. trode l6on reflected primary electrons and on secondary electrons generated within core 22, These electrons may leave the aperture 35 of collector 22 and flow toward cathode 2 with a wide distribution of energies; it is not possible to turn them all back without turningthe enteringprimary electron beam 5; Howy ever, the largest-portion of these undesiredbackward flowing electrons falls in the energy region below 20 percent of the energy of the primary electrons. These backward flowing electrons are returned to the interior of collector 22 by electrode 16 and the energy that would be lost by the power supply system by accelerating them to ground potential .is saved. Accordingly, with the( use ofruggedly mounted suppressor 'electrode 16, the lineal electron beam tube is permitted to operate at a significantly higher power level than would be possible in the absence of electrode 16.

lt is seen that use of the ruggedly mounted suppressor electrode 16 provides a significant advance over prior art electron beam collector systems, permitting more efticienteoperation at higherpower levels than is characteristic of prior art tubes with simple single electrode beam collectors. The suppressor electrode and beam collector system are incorporated in a rugged structure with features assuring long life of a beam type of power tube under repeated cycles of operation without damage to cooperating metal and insulator'parts ofthe sup- 6 pressor electrode andcollector and to bonds supporting those parts. Expansion effects are beneficially directed so that shear stresses on the metal to insulator ture even under severe yoperating conditions. Further, the novel rugged suppressor grid and electron beam collector system'are readily constructed of similar materials and similar parts, so that the same manufacturing technologies may be employed and may be beneficially used for simultaneous construction and assembly of parts of both components and forfinal simultaneous assembly. v l

While the invention has been'described in its pre ferred embodiment, it is .to be understood that the words which have been usedv are words of description rather than limitation and that changes within the purview of the appended claims may be made without departure from the true scope and spirit of the inventionl in its broader aspects.

l claim: l. A linealA electron beam device comprising: electron beam forming means,

high frequency circuit means in energy exchanging relation with said electron beam, vacuum envelopemeans supporting said electron beam forming means and said high frequency cir'- cuit means and having electron beam exit aperture means opposite said high frequency circuit means with' respect to saidelectro'n beam forming means,

metallic casing means sealed in vacuum tight relation with said vacuum envelope 'means adjacent said electron beam exit aperture means, i

disc-shaped gridless apertured suppressor electrode means spaced from said electron beam exit aperture means within a substantially magnetic field free region in said casing means,

first flexible support means for supporting said discshaped gridless apertured suppressor electrode trode means and having axially extending outer surface means,` l second flexible support means for supporting said 'electron beam-collector means at said axially extending outer surface'means in electrically insulating, thermally conducting relation from said casing means, and

first and second conductor means passing in electrically insulating relation through said metallic casing means `for respectively operating. said' 'discshaped gridless. apertured suppressor electrode means at a potential negative with respect to said electron beam-collector means. l 2. Apparatus as in claimvl wherein said first flexible support means comprises:`

first ring-shaped flexible metal fm means having first,

second, and third concentric portions,

second ring-shaped flexible metal fin means having fourth, I fifth, and sixth concentric portions, andV electrically insulating means bonded to said third and fourth portions for forming therewith integral flexible support means.

3. Apparatus as described in claim 2 wherein said electrical insulating means is in the form of a ring with opposed flat parallel sides bonded to said third and fifth portion is in the form of a truncated conical shell.

s l= k i t 

1. A lineal electron beam device comprising: electron beam forming means, high frequency circuit means in energy exchanging relation with said electron beam, vacuum envelope means supporting said electron beam forming means and said high frequency circuit means and having electron beam exit aperture means opposite said high frequency circuit means with respect to said electron beam forming means, metallic casing means sealed in vacuum tight relation with said vacuum envelope means adjacent said electron beam exit aperture means, disc-shaped gridless apertured suppressor electrode means spaced from said electron beam exit aperture means within a substantially magnetic field free region in said casing means, first flexible support means for supporting said disc-shaped gridless apertured suppressor electrode means in electrically insulated relation from said electron beam exit aperture means, hollow electron beam-collector means spaced from said discshaped apertured suppressor electrode means and having axially extending inner surface means for collecting said electrons passing through said electron beam exit aperture means and said disc-shaped gridless apertured suppressor electrode means and having axially extending outer surface means, second flexible support means for supporting said electron beamcollector means at said axially extending outer surface means in electricAlly insulating, thermally conducting relation from said casing means, and first and second conductor means passing in electrically insulating relation through said metallic casing means for respectively operating said disc-shaped gridless apertured suppressor electrode means at a potential negative with respect to said electron beam-collector means.
 2. Apparatus as in claim 1 wherein said first flexible support means comprises: first ring-shaped flexible metal fin means having first, second, and third concentric portions, second ring-shaped flexible metal fin means having fourth, fifth, and sixth concentric portions, and electrically insulating means bonded to said third and fourth portions for forming therewith integral flexible support means.
 3. Apparatus as described in claim 2 wherein said electrical insulating means is in the form of a ring with opposed flat parallel sides bonded to said third and fourth portions of said flexible metal fin means.
 4. Apparatus as described in claim 3 wherein said second portion is in the form of a truncated conical shell.
 5. Apparatus as described in claim 4 wherein said fifth portion is in the form of a truncated conical shell. 